A great variety of adhesive insert layers are known for use in laminated glasses. For example, polyvinylbutyral, polyurethanes and other polymers or copolymers, such as copolymers of vinyl acetate, are used.
Generally, the choice of insert layer depends on the type of laminated glass and its use. Thus, in glasses for automobiles and buildings, polyvinylbutyral is essentially used as the insert, which gives the glass safety properties and determined mechanical properties. For glasses comprising glass-polycarbonate assemblies, the use of a polyurethane base adhesive is known and described in the publication of German patent application DE AS No. 15 94 164. Finally, for soundproofing glasses, the use of a vinyl acetate copolymer as the insert is known according to German patent application DE AS No. 17 09 322.
Although known insert layers exhibit certain interesting properties for well-defined applications, they are unsatisfactory in many regards because of their limited applications and also because of their specific manner of application.
German patent application DE AS No. 15 94 164 discloses the use of a partially polymerized sheet having thermoplastic properties and formed from a thermoplastic polyurethane containing an excess of isocyanate groups. However, the resulting adhesive exhibits a certain sensitivity to temperature. In particular, the elasticity of the adhesive diminishes and then cannot absorb entirely the shearing stresses resulting from the difference in the glass and polycarbonate expansion factors, thus causing deformations of the assembly. Furthermore, the ability of the adhesive to hold small pieces of glass in case of a break leaves much to be desired. Also, stoichiometric mixtures of the isocyanate and polyol components, and especially mixtures containing an excess of the isocyanate component, are relatively expensive.
Similar unsatisfactory properties are also exhibited by the insert layer disclosed in the German patent application DE AS No. 17 09 322, which describes a soundproofing laminated glass comprising a 6 mm glass plate bonded on another sheet of glass or polycarbonate by a layer of adhesive formed from a vinyl acetate copolymer having high viscoelastic properties. Once again, the resulting adhesive exhibits a certain sensitivity to temperature, with a reduction in the elasticity of the adhesive at low temperature. Also, the adhesion is insufficient to hold small pieces of glass in case of breaking of the glass.
One of the objects of the present invention is to provide an insert layer that can be used in laminated glasses with very diverse applications. The insert layer for laminated glasses according to the present invention exhibits adhesion properties that are not affected by great temperature variations and, in case of breaking of the glass, it holds the glass pieces. Also, the insert layer according to the present invention can adequately absorb the shearing stresses due to the differences in expansion rates of the glass laminate components such as, for example, glass and polycarbonate. Another object of the present invention is to provide a laminated glass having excellent soundproofing properties at low manufacturing costs.